The invention relates to an instrument, to an instrument set and to a method for the introduction of an osteochondral transplant, or of an implant which is correspondingly prepared in vitro respectively, in accordance with the preamble of the respective independent claim.
The treatment of cartilage defects with the help of transplantation of osteochondral transplants is a kind of treatment which is increasingly being used in recent times with success. This treatment takes place essentially in that one or more depressions (e.g. blind bores) are first made at the defect location, e.g. by means of a suitable borer. Then transplants such as e.g. bone pegs which have an intact cartilage layer are removed at a harvest location (the harvest location is preferably more or less unstressed). These bone pegs are then introduced into the blind bore which had been made at the defect location. With time the peg grows together with intact cartilage and bone. Depending on the size of the defect a plurality of blind bores can also be made at the defect location and a plurality of pegs used accordingly because the lateral distances (gaps) between the cartilage layer of the transplants and the intact cartilage about the defect location must not become too large. Instead of the transplant a cartilage implant which is cultivated in vitro can also be implanted at the defect location. The surrounding intact cartilage grows together in this case with the cartilage which is cultivated in vitro.
The introduction of a pegxe2x80x94in the following the term xe2x80x9cpegxe2x80x9d will always be used both for a transplant and for an implantxe2x80x94takes place in the known manner that the peg which is located in a passage of the corresponding instrument is pressed out of the instrument into the blind bore with the help of a piston. For this the front surface of the piston is pressed against the surface of the peg facing the piston and the piston is pushed forwardsxe2x80x94the piston is thus located in bodily contact with the cartilage surface of the peg and exerts a force on this cartilage surface in this procedure.
Cartilage cellsxe2x80x94chondrocytesxe2x80x94are sensitive to excessive surface pressings, thus to excessive forces which act on surfaces which are too small. If a surface pressing which is typically permissible for the cartilage cells is exceeded, then the cartilage cells or the cartilage tissue respectively can be damaged. Damaged cartilage hardly regenerates. Moreover, cartilage is also sensitive in regard to deformation, which means that in a non-uniform stressing by forces a cartilage deformation takes place (through which the cartilage can likewise be damaged).
On the other hand cartilage surfaces of pegs are usually convex, seldom concave, almost never planar, often sometimes even slanted (inclined). As a result the cartilage surface and the usually planar front surface of the piston are incongruent and there often results a point or line shaped contact so that at the location of the contact a high surface pressing results. In addition the blind bore at the defect location has a slight under-dimensioning relative to the peg so that the peg sits in a press seating in the blind bore after the introduction. Since the piston is pressed forwards during the introduction of the peg into the blind bore through mild strikings against the proximal end of the piston, the static friction between the peg and the wall of the blind bore must be overcome each time (stop and go). This leads to a still higher stressing of the cartilage surface and can result in damage to the cartilage.
Through the friction between the piston and the cartilage surface, shear strains also arise in addition to the stresses as a result of the striking impulse which can damage the cartilage cells or the cartilage tissue respectively. This is likewise a result of the incongruence of the cartilage surface and the front surface of the piston. Since damaged cartilage hardly regenerates, the result of the transplantationxe2x80x94and thus the benefit to the patientxe2x80x94is in such cases slight. In some cases the introduction of pegs with slanted (inclined) surface even proves impossible.
Here the invention wishes to provide a remedy. The object of the present invention is therefore to propose an instrument and an instrument set respectively by means of which it is possible to drive in an osteochondral transplant or an implant which is correspondingly prepared in vitro independently of the shape of the cartilage surface in a depression which is made at the defect location (e.g. the blind bore mentioned) without damaging the cartilage surface of the transplant or the implant respectively in the process or deforming it (through which the cartilage can likewise be damaged).
This object is satisfied by the method and the instrument or the instrument set respectively such as is characterised by the features of the respective patent claim. Particularly advantageous embodiments result from the features of the subordinate patent claims.
In this it should be mentioned in advance that not only a corporeal piston is to be understood by a xe2x80x9cpistonxe2x80x9d in the sense of the present invention, but rather in general a means for the exerting of forces or of pressure respectively on the buffer medium. This can e.g. also be done with the help of a pump without a corporeal piston coming into contact with the buffer medium.
In accordance with the invention a space for the reception of a buffer medium with a high conformability is provided between the end surface of the piston facing the transplant or implant respectively (in the following for the sake of simplicity reference will be made only to the transplant) and the surface of the transplant facing the piston so that the buffer medium can adapt in an ideal manner at the boundary to the surface of the transplant to the shape of this surface. Furthermore, the buffer medium has an elasticity which is dimensioned in such a manner that no bodily contact between the piston and the transplant exists during the pressing out of the transplant. Through the ideal adaptation of the buffer medium to the shape of the surface of the transplant it is achieved that the surface pressing is as small as possible (the forces are transmitted approximately homogeneously over the entire surface of the transplant). On the other hand a mechanical contact between the piston and the transplant is avoided through the elasticity of the buffer medium so that an incongruent contact of the piston onto the surface of the transplant can not arise. In this way transplants or implants respectively with any desired surface can be driven in into the depressions (e.g. blind bores) at the defect location without it being possible for the transplant surface to be damaged or deformed (and thereby possibly damaged) in the process.
In an advantageous exemplary embodiment the piston is provided with abutment means which define an end position of the piston and prevent a further pushing forward of the piston beyond the end position. Through this it can on the one hand be avoided that the transplant is further stressed by forces beyond a desired end position. If the transplant has namely e.g. been driven in into the depression at the defect location up to a desired depth (not necessarily up to the base of the depression), then it should not be possible to drive in the transplant further into the depression through the further exertion of forces or; respectively, it should not be possible to damage the surface of the transplant through the exertion of excessive surface pressings, such as can arise when the transplant has already been driven in up to the base of the depression, but the transplant is nevertheless stressed with increasingly large surface pressings through further pushing forward of the piston. Here the (preferably adjustable) abutment provides a remedy in that it prevents a further pushing forward of the piston.
In a further advantageous exemplary embodiment the buffer medium is a fluid, in particular a liquid, and the piston is provided with a sealing means which seals off the passage and prevents a backward flowing of fluid in the proximal direction during the pushing forward of the piston in the distal direction. Liquids are particularly preferred because on the one hand they are substantially incompressible and thus reliably prevent a bodily contact between the piston and the surface of the transplant, but however on the other hand adapt ideally to the shape of the surface of the transplant and thus provides for a minimum surface pressing. Body compatible liquids such as e.g. a Ringer solution (a flushing solution which is usually used in the operating room) or a sodium chloride solution (cooking salt) are preferably used as liquids. During the pushing forward of the piston the liquid is driven ahead of the piston and ideally transmits the force to the surface of the transplant independently of the shape of the transplant surface.
In a further development of this exemplary embodiment the sealing means is designed as an O-ring which is arranged in the distal end region of the piston, and indeed proximally to the end surface of the piston facing the transplant. Through this the entire front surface of the piston is available for the transmission of the forces to the liquid, which in turn provides for an ideal transmission of the forces onto the transplant surface.
In a further development of this exemplary embodiment the instrument comprises a sleeve which is provided at its distal end with a cutting edge. In the wall of the sleeve directly following the proximal end of the cutting edge, passage openings are provided which enable an emergence of the fluid as soon as the proximal end of the transplant frees the passage openings during the pressing out of the transplant. In this way it can be achieved that the transplant can no longer or can only to a minimal extent be driven further in after the passing of the passage openings since the liquid can escape through the passage openings and thus the forces are no longer transmitted to the transplant. The operating surgeon notices this through the sudden decrease of the resistance and then knows that the transplant has now been driven in up the desired depth. In this way a kind of non-mechanical xe2x80x9cdepth abutmentxe2x80x9d can thus be realised. In addition mechanical abutment means (see above) can also quite well be provided in order to reliably avoid a bodily contact between the piston and the transplant, should the piston happen to be pushed further forward in spite of the reaching of the non-mechanical xe2x80x9cdepth abutmentxe2x80x9d.
In a further particularly advantageous exemplary embodiment of the instrument the piston can be coupled at its proximal end to a drive which produces a continuous forward thrust of the piston. If namely the transplantxe2x80x94as initially describedxe2x80x94is in each case always driven only a bit of the way with the help of an impulse striking but then comes to rest before it is driven in a further bit of the way with the help of the next impulse striking, then the static friction must be overcome in each case. If in contrast the transplant is continuously driven in, then the static friction need be overcome only once (namely at the beginning) and then only the sliding friction need be overcome, which is lower than the static friction, through which the stress on the transplant surface is further reduced.
Alternatively to the already named fluids, in particular to the liquids, the buffer medium can also be designed as a soft plastic or as a sponge-like plastic, the elastic module of which is smaller than the elastic module of the softest part of the transplant or implant, with it being possible where appropriate for the plastic to be filled with a liquid. As a result of the lower elastic module the buffer medium can first ideally adapt to the shape of the surface of the transplant and then transmits (after a certain compression of the buffer medium has been reached) the forces ideally to the transplant surface. E.g. a balloon which is filled with fluid, in particular liquid, also comes under consideration as a buffer medium.
The instrument set in accordance with the invention comprises an instrument for the removal of a transplant at a harvest location or, respectively, for the removal of the implant which is produced in vitro from a corresponding container. Furthermore, the instrument set comprises an instrument for the production of a depression at the implantation location and an instrument for the introduction of the removed transplant at the implantation location. The instrument for the introduction of the transplant is designed in this in accordance with one of the above explained exemplary embodiments.
In a preferred further development of the instrument set the instrument for the removal of the transplant or the implant respectively is also designed in accordance with one of the above explained exemplary embodiments. In particular it can be the case that the instrument or at least parts thereof can be used both for the removal (extraction) of the transplant and for the introduction (implantation) of the transplant.
Finally the invention also relates to a method for the transplantation of an osteochondral transplant or, respectively, for the implantation of a corresponding implant which is prepared in vitro, in which a depression is first produced at the implantation location for the reception of the transplant or the implant respectively, then the transplant is removed at a harvest location or the implant is removed from a corresponding container respectively, and finally the transplant or the implant respectively is introduced into the depression produced at the implantation location. In this method an instrument in accordance with any one of the above explained exemplary embodiments is used. In an advantageous embodiment of this method, during the introduction of the transplant or the implant respectively, which is located in the passage of the instrument, into the depression from the proximal side, first the buffer medium and then the piston are introduced into the passage so that the enclosed buffer medium drives the transplant or the implant respectively out of the instrument into the depression when the piston is pushed forward in the distal direction. The operating surgeon can thus first bring the instrument together with the transplant which is located in the passage of the instrument into the desired position, then introduce the buffer medium (e.g. the Ringer solution mentioned) and finally place the piston on and push it forward so that with the help of the pressure which is exerted on the buffer medium the transplant is driven in into the depression.